Use the filename to guess mimetype

Since rev 7a3d0da20ddc guess_mimetype test the presence of a dot before the
extension.

issue11541
review421281003
(grafted from d608b8d035f745e40f892101d0fefc86bddd6262)

--HG--
branch : 6.0

src/common.js

@@ -3789,8 +3789,7 @@
 
     Sao.common.download_file = function(data, name, options) {
         if (options === undefined) {
-            var type = Sao.common.guess_mimetype(
-                name ? name.split('.').pop() : undefined);
+            var type = Sao.common.guess_mimetype(name);
             options = {type: type};
         }
         var blob = new Blob([data], options);